Hot Water Temperture Fluctuations on Vaillant Combi

[CorgiKatie]

Hi All, this is my first post, so forgive me if I don't get the protocol quite right...

I'm repairing a Vaillant Turbomax Plus 824e for a client and have come across a problem I've not encountered before.

The boiler was unused for a long period of time and had a couple of standard problems that I resolved (Diverter valve needed changing and AquaSensor had to be cleaned as it wasn't detecting DHW flow properly).

There now seems to be a further problem with the domestic hot water (CH is fine):

When the DHW is run in any circumstances (CH on or off, Warmstart on or off, etc) the temperature fluctuates periodically by around 25C as:

- the burner ignites up,
- gas flow increases until the flow temperature peaks (e.g. 85C)
- then the burner turns off
- boiler waits a few seconds until flow temp reduces (e.g. 60C)
- then the boiler ignites and the cycle starts up again.

The whole cycle takes about 30 seconds.

It doesn't make a difference what the set point for the DHW is on the facia controller.

I can't work out what is happening. There is no fault code and all the diagnostic codes seem to be fine.

The worst thing is that before cleaning the AquaSensor I don't think the problem was there! (Although I may have just missed it).

Does anyone have any tips on what the problem could be and how to resolve this?

Thanks in advance.

Katie
(London)

 

[clf-gas]

Good afternoon Katie and welcome to the forum.

Not over familiar with Vaillants, though I would check NTC.

There is a chap on here, Dave, Gas4you, knows his vaillants inside out.
He will more than likely be in later with sound advice.



PS, get your self signed up to the Combustion Chamber, great help in there with more detail given.



PPS, should of gave you the link, //www.diynot.com/forums/viewtopic.php?t=114690

 

[gas4you]

First I would check the max and min settings on the gas valve.

Other than that it sounds like a classic plate HE blocked.

 

[ChrisR]

FOund one at 16.6mbar burner pressure yesterday. It was turning on and off every couple of seconds. BG carried out a safety check 3 weeks ago
That one needs its plate hex cleaning too!

 

[CorgiKatie]

Thanks all for your advice.

Gas pressures were fine, so I decided to clean the plate HE for a second time...

And problem solved!!

Very strange as I'd already cleaned it, but more gunk came out. I guess there was more debris in the pipes from the time the system wasn't used or i dislodged someting when I clean the AquaSensor

Thanks again and looking forward to taking part in the forum in future.

K